JP2001187880A - Slurry for chemical mechanical polishing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit the staining of polishing pads at CMP(chemical mechanical polishing) of copper metal films. SOLUTION: A slurry for chemical mechanical polishing containing as an essential component secondary particles made of primary particle aggregates comprising θ-alumina, is used as an abrasive grain.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slurry for chemical mechanical polishing used in the manufacture of semiconductor devices, and more particularly to a slurry for chemical mechanical polishing suitable for forming embedded copper wiring.

[0002]

2. Description of the Related Art In recent years, UL has been accelerated in miniaturization and densification.
In forming a semiconductor integrated circuit such as SI, copper has excellent electromigration resistance and low resistance.
It is attracting attention as a very useful electrical connection material.

[0003] At present, formation of wiring using copper is performed as follows due to problems such as difficulty in patterning by dry etching. That is, after a concave portion such as a groove or a connection hole is formed in an insulating film, a barrier metal film is formed, a copper film is formed on the entire surface by a plating method so as to fill the concave portion, and then a chemical mechanical polishing ( The following "CM
Polishing until the surface of the insulating film other than the concave portion is completely exposed by the method (hereinafter referred to as "P") to flatten the surface, and to form an electrical connection portion such as a buried copper wiring in which copper is buried in the concave portion, a via plug, a contact plug and the like. ing.

Hereinafter, a method of forming a buried copper wiring will be described with reference to FIG.

First, as shown in FIG. 3A, a silicon nitride film 3 is formed on a first interlayer insulating film 1 on which a lower wiring 2 is formed.
And a second interlayer insulating film 4 is formed in this order, and a groove having a wiring pattern shape and a concave portion in which a connection hole reaching the lower wiring 2 is formed in a part thereof is formed in the second interlayer insulating film 4 by an ordinary method. Form.

Next, as shown in FIG. 3B, a barrier metal film 4 is formed by a sputtering method. Next, a copper film 5 is formed on the entire surface by plating so that the concave portions are buried. Here, the plating thickness should be equal to or greater than the sum of the groove depth, the connection hole depth, and the manufacturing variation in the plating process.

After that, as shown in FIG. 3C, the copper film 6 is polished by a CMP method using a polishing pad in the presence of a polishing slurry to flatten the substrate surface. Subsequently, FIG.
As shown in (d), polishing is continued until the metal on the second interlayer insulating film 4 is completely removed.

The slurry for CMP for polishing a copper film generally contains an oxidizing agent and abrasive grains as main components. The basic mechanism is that the copper surface is oxidized by the chemical action of the oxidizing agent, and the oxidized surface layer is mechanically removed by abrasive grains.

[0009] As polishing abrasive grains used in a polishing slurry having a high polishing rate of a copper film, primary particles having a desired average particle diameter are easily produced and the polishing rate is high. Up to an average particle size of several hundred nm
The mainstream was to use primary particles of alumina (30 in FIG. 1B).

[0010]

In recent years, as semiconductor integrated circuits have become increasingly finer and denser and the element structure has become more complicated, and the wiring length has to be increased in order to cope with the increase in wiring resistance accompanying the finer wiring. Multilayer wiring for the purpose of shortening
As the number of layers of the logic multi-layer wiring increases, the surface of the substrate becomes more and more uneven, and the level difference becomes larger. Further, the upper wiring portion of the multilayer wiring is used for a power supply wiring, a signal wiring, or a clock wiring, and it is necessary to deepen the wiring groove in order to reduce these wiring resistances and improve various characteristics. is there. Therefore, the thickness of the interlayer insulating film formed on such a substrate surface also increases. In order to form a buried conductive portion such as a buried copper wiring or a via plug in the thick interlayer insulating film, the thickness is large enough to bury a deep recess. It has become necessary to form a copper film. In order to reduce the resistance of thinned wiring and to reduce the resistance of signal wiring and clock wiring to increase the transmission speed,
It is necessary to form a thick wiring in the depth direction, so that a deep concave portion is formed and a thick copper film is formed. Further, even when the power supply wiring is formed of a buried copper wiring, a thick copper film is formed in order to reduce the resistance of the power supply wiring and minimize a potential change. Conventionally, a thick copper film having a thickness of several thousand nm has been formed, whereas a thickness of several hundred nm has been sufficient.

In the case of forming a buried conductive portion by forming a thick copper film as described above, the amount of copper to be removed in one CMP step increases, so that a large amount of copper and copper oxide polishing debris is generated. It adheres and accumulates on the polishing pad surface of the CMP apparatus, and as a result, the polishing rate is reduced to such an extent that polishing is impossible, and it is difficult to finish a uniform polished surface. Current,
In order to improve productivity, it is required to increase the diameter of the wafer. When the diameter of the wafer increases, the copper film area increases in addition to the thickness of the copper. (Hereinafter, polishing waste such as copper or copper oxide generated when polishing a copper-based metal film is referred to as “polishing product”).

On the other hand, for the surface plate of the CMP apparatus, the uniformity of the surface of the surface plate is ensured, the uniform diffusion of the dropped slurry is improved,
There is a limit to the increase in size due to reasons such as restrictions on the installation place of the CMP apparatus, workability of replacing the polishing pad, and ensuring cleanliness in the clean room.

Further, when the polishing amount of copper increases, the throughput decreases at the same polishing rate as when the film thickness is small, so that it is necessary to increase the polishing rate of copper. But,
When the polishing rate of copper is increased, a large amount of polishing products is generated in a short time, so that the adhesion of copper to the polishing pad surface becomes more remarkable.

When a large amount of the polishing product adheres to the polishing pad surface as described above, the polishing pad must be cleaned or replaced every time polishing is completed, and further, the operation is stopped once during the polishing. Since the polishing operation needs to be performed again after the cleaning or replacement of the polishing pad, the throughput is significantly reduced.

Japanese Patent Application Laid-Open No. Hei 10-116804 discloses C
Copper ions generated during the MP accumulate on the polishing pad and re-attach to the wafer surface, deteriorating the flatness of the wafer surface or causing an electrical short circuit. Describes the use of a polishing composition containing a redeposition inhibitor such as benzotriazole. However, this publication describes a problem caused by re-adhesion of copper ions to the wafer surface, but does not describe any problem caused by adhesion of a polishing product to the polishing pad surface. In addition, benzotriazole used as an anti-redeposition agent also acts as an antioxidant (Proc. 2nd Int, by JB Cotton).
ern. Congr. Metallic Corr
osion, p. 590, 1963; Chadw
Ick et al., CorrosionSci. , Volume 18,
39, 1978; Notoya, Takeo, Rust Prevention Management, No. 2
6, No. 3, p. 74, 1982; Heihachiro Okabe, ed., "Development and Latest Technology of Petroleum Product Additives", 1998, CMC, pp. 77-82), for reducing the polishing rate of copper , The amount of addition is limited. Further, benzotriazole is originally added to prevent dishing (Japanese Patent Application Laid-Open No. 8-83780,
When priority is given to prevention of dishing, adjustment of the addition amount is restricted.

Japanese Patent Application Laid-Open No. 10-44047 discloses a polishing abrasive having a size distribution of less than about 1.0 μm and a size distribution of about 0.4 μm.
an aggregate of a metal oxide having an average aggregate diameter of less than m.
Alternatively, use of spherical particles of individually independent metal oxides having primary particles of less than 0.4 μm is described.
However, the invention described in this publication aims at suppressing surface defects and contamination due to CMP, forming uniform metal layers and thin films, and controlling selectivity between barrier films and insulating films. This publication does not describe any problem caused by the adhesion of the polishing product to the polishing pad surface. Further, as the exemplified alumina abrasive, only general precipitated alumina and fumed alumina are described, but there is no description about θ alumina. Further, copper is only exemplified as a connection material, and only Al is used in the embodiment.

Japanese Patent Application Laid-Open No. 10-163141 discloses θ-alumina as abrasive grains. However, in this publication, [theta] -alumina is merely described as an example of aluminum oxide, such as [alpha] -alumina, and nothing is described about secondary particles of [theta] -alumina. Further, the invention described in this publication provides a polishing composition that prevents scratching and dishing, has a high polishing rate for a copper film, has an appropriate selectivity, and has good storage stability. For the purpose of
There is no description about suppressing the adhesion of polishing products to the polishing pad surface.

JP-A-10-46140 discloses a composition for chemical mechanical polishing comprising a specific carboxylic acid, an oxidizing agent and water, wherein the pH is adjusted to 5 to 9 with an alkali. Is described, in the examples,
A polishing composition (Example 7) containing citric acid as a carboxylic acid and aluminum oxide as polishing abrasive grains is illustrated. However, this publication only describes the effects of adding an organic acid such as citric acid on improving the polishing rate and preventing the occurrence of dishing due to corrosion marks.

JP-A-11-21546 discloses a slurry for chemical and mechanical polishing containing urea, an abrasive, an oxidizing agent, a film forming agent and a complexing agent. Hydrogen peroxide is used as an agent, benzotriazole is used as a film-forming agent, and citric acid is used as a complexing agent. However, the effect of adding the complexing agent is as follows.
Only disturbing the passivation layer formed by a film forming agent such as benzotriazole and limiting the depth of the oxidized layer are described.

Therefore, an object of the present invention is to suppress the adhesion of a polishing product to a polishing pad even when a large amount of copper-based metal is polished, and to achieve a desired polishing amount once without interrupting the polishing operation. An object of the present invention is to provide a chemical mechanical polishing slurry which can be polished well by the above polishing operation.

[0021]

SUMMARY OF THE INVENTION The present invention provides a slurry for chemical mechanical polishing for polishing a copper-based metal film,
The present invention relates to a slurry for chemical mechanical polishing characterized by containing θ-alumina containing, as main components, secondary particles obtained by aggregating primary particles as abrasive grains, an oxidizing agent and an organic acid.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described.

The slurry for chemical mechanical polishing of the present invention (hereinafter, also referred to as "polishing slurry"), as shown in FIG. 1 (a), is formed by aggregating primary particles 10 as abrasive grains.
Θ alumina containing the primary particles 20 as a main component (hereinafter referred to as “containing 2
Secondary particles θ alumina). According to such a polishing slurry, even when polishing a thick or large-area copper-based metal film, that is, even when polishing a large amount of copper-based metal in one polishing operation,
The adhesion of polishing products to the polishing pad can be suppressed,
Good polishing can be continuously performed without interrupting the polishing operation. In this specification, a copper-based metal refers to copper or an alloy containing copper as a main component.

The content of the secondary particles of the secondary-particle-containing θ-alumina is set at 60% based on the total amount of the secondary-particle-containing θ-alumina from the viewpoint that the adhesion of the polishing product to the polishing pad is more sufficiently suppressed.
It is preferably at least 65 mass%, more preferably at least 65 mass%, even more preferably at least 70 mass%.

The average particle size of the secondary particles is 0.0
It is preferably at least 5 μm, more preferably at least 0.07 μm, even more preferably at least 0.08 μm. As an upper limit,
It is preferably at most 0.5 μm, more preferably at most 0.4 μm, even more preferably at most 0.3 μm.

Further, in the whole secondary particles of the θ-alumina,
The proportion occupied by the secondary particles having a particle size of 0.05 μm or more and 0.5 μm or less is preferably 50% by mass or more, more preferably 55% by mass or more, and even more preferably 60% by mass or more.

In addition, the secondary particle-containing θ-alumina is preferably substantially free of primary particles and secondary particles having a particle diameter of preferably 2 μm, more preferably 1.5 μm, and still more preferably 1 μm. .

The average particle size of the primary particles constituting the secondary particles of θ-alumina as described above is preferably 0.005 μm or more, more preferably 0.007 μm or more, and 0.008 μm or more.
μm or more is more preferable. The upper limit is preferably 0.1 μm or less, more preferably 0.09 μm or less.
08 μm or less is more preferable.

The average particle diameter of the primary particles constituting the secondary particles and the θ-alumina in the present invention is much smaller than the primary particles of α-alumina generally used as conventional abrasive grains. The average particle size of the secondary particles composed of such primary particles can be adjusted to the same level as the average particle size of the conventional α-alumina primary particles. Then, CMP is performed using a polishing slurry containing θ-alumina containing the secondary particles as a main component (secondary particle θ-alumina) as a main component of the abrasive grains.
Is performed, the contact area between the polished surface of copper and the primary particles constituting the secondary particles is small, so that the polishing products generated by mechanical removal are small. Further, the polishing product is:
Since the particles are finely pulverized due to voids and irregularities between the primary particles constituting the secondary particles, a finer polishing product is obtained.

The secondary particle-containing θ-alumina is the conventional α-alumina.
Since it has a larger surface area than the primary particles of alumina, it has good dispersibility, and therefore, formation of giant particles due to association of secondary particles is suppressed. For this reason, generation of a large-sized polishing product generated from the polished surface by being scraped off by the giant particles is suppressed.

For the above reasons, in the CMP using the polishing slurry of the present invention, since the generated polishing product is minute, the polishing product hardly causes clogging on the polishing pad surface, and at the same time, the fine polishing The product is
It is easily washed away by the continuously supplied polishing slurry. Therefore, even when a large amount of copper is polished, contamination of the polishing pad is suppressed.

In the CMP using the polishing slurry of the present invention, the generation of scratches on the polished surface is suppressed in addition to the effect of suppressing the contamination of the polishing pad. Since the secondary particle-containing θ-alumina can be deformed by a polishing load (contact pressure of the polishing pad) from the polishing pad, stress concentration does not occur at a contact portion between the polishing surface and the primary particles constituting the secondary particles. As a result, the occurrence of scratches is suppressed without the polished surface being greatly scooped.

The Mohs hardness of θ-alumina is 7, while the Mohs hardness of α-alumina is 9. That is, since θ-alumina has a lower hardness than α-alumina and has an appropriate hardness for polishing a soft metal such as copper, scratches hardly occur.

Further, since the secondary particles of the θ-alumina secondary particles have a large surface area, they are excellent in dispersibility, and since the primary particles are extremely fine, the polishing slurry of the present invention is stable for a long time. It also has the characteristic of having excellent properties.

The average particle diameter of the polishing abrasive grains, the ratio of the abrasive grains having a specific range of particle diameters, and the maximum particle diameter are determined by measuring the particle size distribution of the polishing abrasive grains by a light scattering method. It can be calculated by performing statistical processing. Further, the particle size distribution of the abrasive grains can be determined by measuring the particle diameters of a large number of abrasive grains using an electron microscope.

The production of θ-alumina can be carried out by removing water of crystallization from a colloid comprising a hydrate or hydroxide of a salt containing Al by a heat treatment at a controlled rate of temperature rise. Aggregates formed by fusing the contact portions of the adjacent primary particles during the heat treatment are secondary particles.
In the production of θ-alumina, fine colloidal particles having a controlled particle size can be prepared, so that fine primary particles having an average particle size and a particle size distribution suitable for the present invention can be obtained. For this reason, secondary particles of θ-alumina having the same particle size as the primary particles of conventional α-alumina can be formed. Further, since the bonding force of the fusion between the primary particles formed during the heat treatment is an appropriate value, the bonding between some of the primary particles can be broken by dispersion under appropriate conditions. Thus, secondary particles having a particle size suitable for the present invention can be formed.

Including 2 contained in the polishing slurry of the present invention
The secondary particle θ-alumina can be produced by dispersing the θ-alumina formed as described above in a dispersion medium under appropriate conditions. The θ-alumina produced by the heat treatment of the colloid has an average particle size of 10
It consists of a huge aggregate of about μm. This is added to the aqueous medium in a range of 10% by mass to 70% by mass. If necessary, a dispersant may be added in a range of 0.01% by mass or more and 10% by mass or less. The addition amount of the θ-alumina and the dispersant affects the particle size of the obtained secondary particles.

The dispersion can be carried out using an ultrasonic disperser, a bead mill disperser, a ball mill disperser, a kneader disperser or the like. Among these, it is preferable to use a bead mill disperser or a ball mill disperser because secondary particles having a desired particle size can be formed stably. In addition, the particle size is 2 μm
In order to remove the above particles, these dispersers may be provided with a filter mechanism.

The dispersion time affects the particle size distribution of the secondary particles,
In order to obtain secondary particles having a particle size distribution with high monodispersity, dispersion is performed preferably for 140 minutes or more, more preferably 150 minutes or more, and still more preferably 180 minutes or more. Also,
The upper limit of the dispersion time is preferably 400 minutes or less, more preferably 350 minutes or less, and even more preferably 300 minutes or less, in order to suppress the inclusion of foreign matter.

As the dispersant, at least one of a surfactant type and a water-soluble polymer type dispersant can be used.

Examples of the surfactant-based dispersant include anionic, cationic, amphoteric and nonionic surfactants. As anionic surfactants, sulfonic acid, sulfate, carboxylic acid, phosphate,
Soluble salts such as phosphonic acid can be used. These soluble salts include, for example, sodium alkylbenzene sulfonate (ABS), sodium dodecyl sulfate (S
DS), sodium stearate, sodium hexametaphosphate and the like. Examples of the cationic surfactant include amine salts containing a tertiary amine capable of forming a salt, modified salts thereof, quaternary ammonium salts, onium compounds such as phosphonium salts and sulfonium salts, pyridinium salts, Cyclic nitrogen compounds such as quinolinium salts and imidazolinium salts, and heterocyclic compounds can be used. Examples of these cationic surfactants include cetyltrimethylammonium chloride (CTAC), cetyltrimethylammonium bromide (CTAB), cetyldimethylbenzylammonium bromide, cetylpyridinium chloride, dodecylpyridinium chloride, and alkyldimethylchlorobenzyl chloride. Examples thereof include ammonium and alkylnaphthalenepyridinium chloride.

Examples of the nonionic surfactant include those obtained by addition-polymerizing ethylene oxide to a fatty acid such as polyethylene glycol fatty acid ester, polyoxyethylene alkyl ether, or polyoxyethylene alkylphenyl ether; ether-type nonionic surfactants; Polyethylene glycol condensation type surfactants can be used. As these nonionic surfactants, for example,
POE (10) monolaurate, POE (10) monostearate, POE (25) monostearate, POE
(40) monostearate, POE (45) monostearate, POE (55) monostearate, POE (2
1) Lauryl ether, POE (25) lauryl ether, POE (15) cetyl ether, POE (20) cetyl ether, POE (23) cetyl ether, POE
(25) Cetyl ether, POE (30) cetyl ether, POE (40) cetyl ether, POE (20) stearyl ether, POE (2) nonyl phenyl ether, POE (3) nonyl phenyl ether, POE
(5) Nonyl phenyl ether, POE (7) nonyl phenyl ether, POE (10) nonyl phenyl ether, POE (15) nonyl phenyl ether, POE
(18) nonyl phenyl ether, POE (20) nonyl phenyl ether, POE (10) octyl phenyl ether, POE (30) octyl phenyl ether,
POE (6) sorbitan monooleate, POE (2
0) sorbitan monooleate, POE (6) sorbitan monolaurate, POE (20) sorbitan monolaurate, POE (20) sorbitan monopalmirate,
POE (6) sorbitan monostearate, POE (2
0) sorbitan monostearate, POE (20) sorbitan tristearate, POE (20) sorbitan trioleate, POE (6) sorbitan monooleate, POE (20) sorbitan monooleate. Here, POE is polyoxyethylene, and the number in parentheses represents the number of repeating units —CH ₂ CH ₂ O—.

As the amphoteric surfactant, at least one kind of atomic group selected from the group consisting of —COOH group, —SO ₃ H group, —OSO ₃ H group, and —OPO ₃ H ₂ group which becomes an anion in the molecule is used. A compound containing a tertiary amine or a quaternary ammonium as an atomic group that becomes a cation can be used. For example, there are betaine, sulfobetaine, sulfate betaine type, and more specifically, betaine lauryldimethylaminoacetate, N-coconut fatty acid acyl-N-carboxymethyl-N-hydroxyethylenediamine sodium, and the like.

As the water-soluble polymer dispersant,
There are ionic polymers and nonionic polymers. Examples of the ionic polymer include alginic acid or a salt thereof, polyacrylic acid or a salt thereof, polycarboxylic acid or a salt thereof, cellulose, carboxymethyl cellulose, hydroxylethyl cellulose, and the like.As the nonionic polymer, polyvinyl alcohol, Polyvinylpyrrolidone, polyethylene glycol, polyacrylamide and the like can be mentioned.

The weight average molecular weight of the water-soluble polymer dispersant is preferably 100 or more, more preferably 500 or more, even more preferably 1000 or more, and the upper limit is 10 or more.
It is preferably at most 0000, more preferably at most 80,000, even more preferably at most 50,000. When the weight average molecular weight is within this range, the increase in viscosity of the obtained polishing slurry can be suppressed, and secondary particles having a good particle size distribution can be formed.

As long as the effect of the secondary particle-containing θ-alumina is not impaired, other abrasive grains may be used together if necessary. Other polishing abrasives include alumina other than θ-alumina such as α-alumina and δ-alumina, silica such as fumed silica and colloidal silica, titania, zirconia, germania, ceria, and metal oxide polishing abrasives thereof. Or a mixture of two or more selected from the group consisting of:

The content of the secondary particle-containing θ-alumina is preferably at least 1% by mass, more preferably at least 3% by mass, based on the entire slurry for chemical mechanical polishing, and the upper limit is 3%.
0 mass% or less is preferable and 10 mass% or less is more preferable. When the polishing slurry contains two or more types of abrasive grains, the total content of each abrasive grain is preferably at least 1% by mass, and more preferably at least 3% by mass, based on the entire slurry for chemical mechanical polishing. More preferably, the upper limit is preferably 30% by mass or less, more preferably 10% by mass or less.

Oxidation contained in the polishing slurry of the present invention
As an agent, water-soluble
It can be used by selecting from oxidizing agents. For example, heavy money
Shall not cause contamination of the genus ions
And H_TwoO_Two, Na_TwoO_Two, Ba_TwoO_Two, (C₆H_FiveC)_TwoO_Twoetc
Peroxide, hypochlorous acid (HClO), perchloric acid, nitric acid
Organic peroxidation of acids, ozone water, peracetic acid, nitrobenzene, etc.
Things can be mentioned. Above all, metal components
Hydrogen peroxide (H _TwoO_Two)
Is preferred. Oxidation contained in the polishing slurry of the present invention
The amount of the slurry should be sufficient to obtain a sufficient addition effect.
0.01% by mass or more based on the total amount is preferable,
% By mass or more, more preferably 0.1% by mass or more.
Good. Upper limit is appropriate for suppressing dishing and polishing rate
From the viewpoint of adjusting to a suitable value, it is preferably 15% by mass or less.
0 mass% or less is more preferable. In addition, like hydrogen peroxide
When using an oxidizing agent that is relatively easily deteriorated with time,
An oxidant-containing solution having a predetermined concentration and this oxidant-containing solution
By adding it, it becomes a predetermined polishing slurry
Prepare the composition separately and mix both immediately before use.
You may.

As an organic acid, it promotes oxidation of an oxidizing agent,
In order to perform stable polishing, a carboxylic acid or an amino acid can be used as a proton donor.

The carboxylic acids include oxalic acid, malonic acid, tartaric acid, malic acid, glutaric acid, citric acid, maleic acid, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, acrylic acid, lactic acid, succinic acid, nicotinic acid , Their salts, and mixtures of these carboxylic acids.

Particularly, citric acid is preferable because it easily forms a complex with copper ions and suppresses contamination of the polishing pad. The synergistic effect of the complex-forming action of citric acid and the action of the secondary particle-containing θ-alumina further suppresses polishing pad contamination.

Examples of the amino acid include L-glutamic acid, D-glutamic acid, L-glutamic acid monohydrochloride,
Sodium L-glutamate monohydrate, L-glutamine, glutathione, glycylglycine, DL-alanine, L-alanine, β-alanine, D-alanine, γ-
Alanine, γ-aminobutyric acid, ε-aminocaproic acid, L
-Arginine monohydrochloride, L-aspartic acid, L-aspartic acid monohydrate, potassium L-aspartate, L
-Calcium aspartate trihydrate, D-aspartic acid, L-titrulline, L-tryptophan, L-threonine, L-arginine, glycine, L-cystine, L-
Cysteine, L-cysteine hydrochloride monohydrate, L-oxyproline, L-isoleucine, L-leucine, L-lysine monohydrochloride, DL-methionine, L-methionine, L
-Ortinine hydrochloride, L-phenylalanine, D-phenylglycine, L-proline, L-serine, L-tyrosine, L-valine, and mixtures of these amino acids.

The content of the organic acid is preferably 0.01% by mass or more, more preferably 0.05% by mass or more based on the total amount of the polishing slurry, from the viewpoint of obtaining a sufficient effect as a proton donor. . The upper limit is preferably 5% by mass or less, more preferably 3% by mass or less, from the viewpoint of suppressing dishing and adjusting the polishing rate to an appropriate level. In addition, when the polishing slurry contains a plurality of organic acids, the above content means the sum of the content of each organic acid.

An antioxidant may be further added to the polishing slurry of the present invention. The addition of the antioxidant facilitates adjustment of the polishing rate of the copper-based metal film, and also suppresses dishing by forming a coating on the surface of the copper-based metal film.

Examples of the antioxidant include benzotriazole, 1,2,4-triazole, benzofuroxane, 2,1,3-benzothiazole, o-phenylenediamine, m-phenylenediamine, catechol, o-amino Phenol, 2-mercaptobenzothiazole, 2
-Mercaptobenzimidazole, 2-mercaptobenzoxazole, melamine and derivatives thereof. Among them, benzotriazole and its derivatives are preferred. As a benzotriazole derivative, a benzene ring has a hydroxyl group, an alkoxy group such as methoxy or ethoxy, an amino group, a nitro group, a methyl group or an ethyl group,
Examples include an alkyl group such as butyl or a substituted benzotriazole having a halogen substituent such as fluorine, chlorine, bromine or iodine. Further, naphthalene triazole, naphthalene bistriazole, substituted naphthalene triazole substituted in the same manner as described above, and substituted naphthalene bistriazole can be exemplified.

The content of such an antioxidant is as follows:
From the viewpoint of obtaining a sufficient effect of addition, the content is preferably 0.0001% by mass or more based on the total amount of the polishing slurry, and 0.001% by mass or less.
% By mass or more is more preferable. The upper limit is preferably 5% by mass or less from the viewpoint of adjusting the polishing rate to an appropriate level.
5 mass% or less is more preferable.

The lower limit of the pH of the polishing slurry of the present invention is preferably pH 3 or higher, more preferably pH 4 or higher, and the upper limit is pH 9 from the viewpoints of polishing rate, corrosion, slurry viscosity, and dispersion stability of the abrasive. The following is preferable, p
H8 or less is more preferable.

The pH of the polishing slurry can be adjusted by a known method, for example, by directly adding an alkali to a slurry in which abrasive particles are dispersed and a carboxylic acid is dissolved. Alternatively, some or all of the alkali to be added may be added together with an alkali salt of a carboxylic acid. Examples of the alkali used include hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide, carbonates of alkali metals such as sodium carbonate and potassium carbonate, ammonia, and amines.

The polishing slurry of the present invention may contain various additives, such as a buffer and a viscosity modifier, which are generally and generally added to the polishing slurry, as long as the properties are not impaired.

In polishing a substrate having a copper-based metal on its surface, the polishing slurry of the present invention can be used in a single polishing operation to at least 2 × 10 ⁻⁴ g of copper-based metal per cm ² of a polishing pad.
It can be suitably used when performing MP, and 1 ×
Even if the polishing is 10 ^-3 g or more, or even 1 × 10 ^-2 g or more, the polishing pad can be suitably used without contamination of the polishing pad.

The polishing slurry of the present invention preferably has a composition ratio adjusted so that the polishing rate of the copper-based metal film is preferably at least 300 nm / min, more preferably at least 400 nm / min. Further, the polishing slurry of the present invention,
The polishing rate of the copper-based metal film is preferably 15
It is preferable to adjust the composition ratio so as to be not more than 00 nm / min, more preferably not more than 1000 nm / min.

In an apparatus for performing CMP, a wafer on which a copper-based metal film is formed is set on a wafer carrier of a spindle. The surface of the wafer is brought into contact with a polishing pad made of porous urethane stuck on a rotating plate (platen), and the wafer is polished while the polishing slurry is supplied to the polishing pad surface from a polishing slurry supply port. Spin both pads to polish. If necessary,
The surface of the polishing pad is conditioned by bringing the pad conditioner into contact with the surface of the polishing pad.

At the stage when the CMP is completed, the supply of the polishing slurry is stopped by closing the polishing slurry supply port, and the cleaning liquid is supplied from another supply port to perform rinsing for 15 to 30 seconds. Thereafter, megasonic cleaning is performed in a state where the wafer is not dried, the polishing slurry is removed, and the wafer is dried.

In the polishing slurry of the present invention described above, a barrier metal film is formed on an insulating film having a concave portion such as a groove or an opening, and a copper-based metal film is formed on the insulating film so as to fill the concave portion. It is most effectively used when the substrate formed on the entire upper surface is subjected to CMP to form an electrical connection such as a buried wiring, a via plug, or a contact plug. Examples of the barrier metal film include Ta, TaN, Ti, and TiN. As an insulating film, a silicon oxide film, BPSG
And an insulating film such as a SOG film. As the copper-based metal film, in addition to the copper film, silver, gold, platinum, titanium, tungsten,
Examples include a copper alloy film containing various conductive metals such as aluminum.

According to the polishing slurry of the present invention, even when a large amount of copper is polished due to a thick copper film or a large area, adhesion of polishing products to a polishing pad is suppressed, and polishing is performed. A large amount of copper-based metal can be removed without interrupting operation.
CMP can be performed well by a moderate polishing operation. According to the polishing slurry of the present invention, since a polishing product is suppressed from adhering not only to the polishing pad surface but also to the polishing surface, a problem on element characteristics such as an electrical short circuit between wirings does not occur. In addition, a polished surface having excellent smoothness can be formed.

[0066]

The present invention will be described in more detail with reference to the following examples.

(Preparation of Secondary Particle-Containing θ-Alumina Dispersion) The secondary particle-containing θ-alumina was prepared using Sumitomo Chemical Co., Ltd. θ-alumina (AKP-G008). Observation of the pre-prepared θ-alumina by SEM revealed that a large number of primary particles (average particle diameter 0.05 μm) having a minimum particle diameter of 0.03 μm and a maximum particle diameter of 0.08 μm consisted of aggregates bonded by fusion. It turns out. The average particle size of this aggregate is 10 μm.
m. In some cases, a very small amount of primary particles with respect to the minimum particle size and a very small amount of primary particles with respect to the maximum particle size were observed. Was not affected at all, and did not contribute to the value of the average particle size at all.

Next, the dispersant AQUALIC HL415 manufactured by Nippon Shokubai was mixed with ion-exchanged water so as to have a concentration of 4% by mass, and then the θ-alumina before preparation was mixed with the mixture to have a concentration of 40% by mass. The obtained liquid mixture was dispersed at a rotation speed of 1,000 times / minute by a bead mill (Super Mill) manufactured by Inoue Seisakusho. The dispersion time was varied between 20 and 400 minutes to prepare a plurality of dispersions.

With respect to the θ-alumina contained in each dispersion, the particle size distribution of the whole particles was measured by a particle size distribution analyzer LS-230 manufactured by Beckman Coulter. The maximum particle size was determined from the particle size distribution of the whole obtained particles. The particle size distribution of the secondary particles was calculated by subtracting the particle size distribution of the primary particles from the particle size distribution of the whole particles. The average particle size of the secondary particles was determined by performing statistical processing on the particle size distribution of the obtained secondary particles. Further, with respect to the dispersion liquid having a dispersion time of 200 minutes, the content of the secondary particles with respect to the whole
The ratio of secondary particles of m or less to the entire secondary particles was also determined.

FIG. 2 shows the θ in the dispersion at each dispersion time.
The maximum particle size of the alumina (●) and the average particle size of the secondary particles (○) are shown. 3μ when the dispersion time is 120 minutes or less
However, when the dispersion time was 140 minutes or more, the maximum particle size was 1 μm or less.

When the dispersion time is 200 minutes, the average particle size of the secondary particles is 0.15 μm, the maximum particle size is 0.6 μm,
Secondary particles The content of secondary particles with respect to the entirety of alumina is 7
The ratio of secondary particles having a particle size of 4% by mass and a particle size of 0.05 μm or more and 0.5 μm or less in the whole secondary particles was 62% by mass. In addition, no foreign matter was particularly confirmed.

Example 1 Of the dispersions obtained as described above, those having a dispersion time of 200 minutes were used.
Polishing slurry 1 having a pH of 7 was prepared, which contained 03% by mass of secondary particles θ-alumina, 0.47% by mass of citric acid, and 1.9% by mass of H ₂ O ₂ . The pH was adjusted with ammonia, and H ₂ O ₂ was added immediately before CMP.

Next, on a 6-inch wafer (silicon substrate) on which semiconductor elements such as transistors are formed (not shown), as shown in FIG. After an oxide film 1 is formed, a silicon nitride film 3 and a second silicon oxide film 4 having a thickness of about 1.5 μm are formed thereon, and the second silicon oxide film 3 is formed by a conventional method such as lithography and patterning by etching. A wiring groove was formed in the oxide film 4 and a connection hole reaching the lower wiring 2 was formed in a part of the groove. Next, a thickness of 50 nm is formed by a sputtering method.
After forming a Ta film having a thickness of about 50 nm and subsequently forming a copper film having a thickness of about 50 nm by a sputtering method, a copper film 6 having a thickness of about 2 μm was formed by a plating method.

The copper film is formed by polishing the slurry using polishing slurry 1.
MP. The CMP was performed by using Model SH-24 manufactured by Speedfam Ipec. A polishing pad (IC 1400 manufactured by Rodel Nitta) having a diameter of 61 cm (24 inches) was attached to a surface plate of the polishing machine. The polishing conditions were as follows: polishing pad contact pressure (polishing pressure): 27.6.
kPa, the polishing area of the polishing pad: 1820 cm ² , the number of rotations of the platen: 55 rpm, the number of rotations of the carrier: 55 rpm, and the supply amount of the slurry polishing liquid: 100 ml / min. 2 copper films
Dirt on the polishing pad after polishing by about μm was evaluated visually and by a polishing rate.

The above copper film was polished by about 2 μm. The polishing rate was constant until the polishing was completed, and the polishing could be performed stably. Thereafter, the dirt on the polishing pad was visually evaluated, and it was found that the polishing product hardly adhered to the polishing pad. Further, when the polished surface was observed by SEM, the occurrence of scratches was also suppressed.

Example 2 A polishing slurry 2 was prepared in the same manner as the polishing slurry 1 except that malic acid was used instead of citric acid. Using this polishing slurry 2,
CMP was performed in the same manner as described above. The polishing rate was constant until the polishing was completed, and the polishing could be performed stably.
Thereafter, when the contamination of the polishing pad was evaluated in the same manner as described above, it was found that the polishing product hardly adhered to the polishing pad. Further, when the polished surface was observed by SEM, the occurrence of scratches was also suppressed.

(Comparative Example 1) Commercially available α instead of θ alumina
A polishing slurry 3 was prepared in the same manner as the polishing slurry 2 except that alumina was used. Using this polishing slurry 3, CMP was performed in the same manner as described above to evaluate the contamination of the polishing pad. As a result, it was found that a large amount of polishing products had adhered to the polishing pad.

[0078]

As is clear from the above description, according to the polishing slurry of the present invention, even when the amount of copper polished is large because the copper film is thick or large, the polishing slurry can be applied to the polishing pad. The desired amount of polishing can be satisfactorily performed in a single polishing operation without interrupting the polishing operation.
it can.

[Brief description of the drawings]

FIG. 1 is a schematic view for explaining the structure of alumina polishing abrasive grains.

FIG. 2 is a diagram showing how the particle size of θ-alumina changes with dispersion time.

FIG. 3 is a process cross-sectional view for describing a method of forming a buried copper wiring.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 first interlayer insulating film 2 lower layer wiring 3 silicon nitride film 4 second interlayer insulating film 5 barrier metal film 6 copper film 10 primary particles of θ-alumina 20 secondary particles of θ-alumina 30 primary particles of α-alumina

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Tomoko Waki, Inventor 5-7-1 Shiba, Minato-ku, Tokyo Inside NEC Corporation (72) Inventor Tetsuyuki Itakura 5-1-1, Taito, Taito-ku, Tokyo Tokyo Inside Magnetic Printing Co., Ltd. (72) Inventor Shin Sakurai 1-5-1, Taito, Taito-ku, Tokyo Tokyo Magnetic Printing Co., Ltd. (72) Kenichi Aoyagi 1-1-5-1, Taito, Taito-ku, Tokyo Tokyo F term (reference) in Magnetic Printing Co., Ltd. 3C058 AA07 CA01 CB01 CB03 DA02 DA12

Claims (12)

[Claims] 1. A slurry for chemical mechanical polishing for polishing a copper-based metal film, wherein θ-alumina containing, as a main component, secondary particles obtained by aggregating primary particles as polishing abrasive grains;
A slurry for chemical mechanical polishing comprising an oxidizing agent and an organic acid. 2. The content of the θ-alumina is 1% by mass or more and 30% by mass with respect to the entire slurry for chemical mechanical polishing.
The slurry for chemical mechanical polishing according to claim 1, wherein: 3. The content of the secondary particles of the θ-alumina is:
The slurry for chemical mechanical polishing according to claim 1 or 2, wherein the slurry is 60% by mass or more based on the whole of the θ-alumina. 4. The slurry for chemical mechanical polishing according to claim 1, wherein the secondary particles of the θ-alumina have an average particle diameter of 0.05 μm or more and 0.5 μm or less. . 5. The θ-alumina contains 50% by mass or more of secondary particles having a particle size of 0.05 μm or more and 0.5 μm or less based on the entire secondary particles.
5. The slurry for chemical-mechanical polishing according to any one of items 4 to 4. 6. The chemical mechanical polishing apparatus according to claim 1, wherein the θ alumina does not substantially contain primary particles and secondary particles having a particle size larger than 2 μm. slurry. 7. The slurry for chemical mechanical polishing according to claim 1, wherein the primary particles of the θ alumina have an average particle diameter of 0.005 μm or more and 0.1 μm or less. . 8. The content of the organic acid is 0.01% by mass or more and 5% by mass with respect to the whole slurry for chemical mechanical polishing.
The slurry for chemical mechanical polishing according to any one of claims 1 to 7, wherein: 9. The chemical machine according to claim 1, wherein the slurry contains 0.01% by mass or more and 5% by mass or less of citric acid based on the whole slurry for chemical mechanical polishing. Polishing slurry. 10. The slurry for chemical mechanical polishing according to claim 1, wherein the pH is 4 or more and 8 or less. 11. The method according to claim 1, wherein the content of the oxidizing agent is 0.01% by mass or more and 15% by mass or less based on the whole slurry for chemical mechanical polishing. Slurry for chemical mechanical polishing. 12. The slurry for chemical mechanical polishing according to claim 11, wherein the slurry for chemical mechanical polishing contains 0.0001% by mass or more and 5% by mass or less of an antioxidant based on the whole slurry for chemical mechanical polishing. .